[petsc-users] KSP diverging

Matthew Knepley knepley at gmail.com
Fri Dec 23 07:43:54 CST 2011

On Thu, Dec 22, 2011 at 7:51 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> On Thu, Dec 22, 2011 at 19:46, Matthew Knepley <knepley at gmail.com> wrote:
>> dtol failure is impossible for GMRES (and CG). Consider checking with
>> that.
> Well, if you turn of restarts in GMRES and if orthogonalization is working
> correctly.

Even if you lose orthogonality, it will just stagnate since you always have
the solution
from the first few vectors. Likewise, I do not see how you can get an
diverging sequence
from restarting since you always have the last residual, you just stagnate.


What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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